There is a growing need for competitive local exchange carriers to manage remote power control functions of internetworking devices at telephone company (telco) central offices. Competitive local exchange carriers (CLECs), incumbent local exchange carriers (ILECs), independent telephone companies, and other next generation service providers are now all offering a digital subscriber line (DSL) service that promises high-speed Internet access for both homes and businesses. DSL is expected to replace integrated services digital network (ISDN) equipment and lines, and DSL competes very well with the T1 line that has historically been provided by ILECs. A DSL drop costs about $40-60 per month, and is expected to quickly become the dominant subscriber-line technology.
The DSL service is provided by a switch that is co-located in a telco central office, that is, a digital subscriber line access multiplexer (DSLAM). Many new competitive local exchange carriers are now deploying DSL service in several states. They are installing digital subscriber line access multiplexers in many locations. Such digital subscriber line access multiplexers are now available from a number of different manufacturers, for example, Paradyne, Copper Mountain, Ascend, etc.
Nearly all such digital subscriber line access multiplexers are powered by 48-VDC battery power and all have operator console ports. And for emergencies, these DSLAMs usually have two independent 48-VDC battery power supplies, for example, an A-channel and a B-channel. Most commercial DSLAMs are also controlled by large operating systems that host various application software. Unfortunately, this means most DSLAMs have the potential to fail or lock-up, for example, due to some software bug.
When a digital subscriber line access multiplexer does lock-up, the time-honored method of recovering is to cycle the power, that is, reboot. But when a digital subscriber line access multiplexer is located at a telco central office, such location practically prevents it being easy to reboot manually.
There are many large router and ATM switch farms around the country that are equipped by the leading vendors, for example, Cisco, Bay Networks/Nortel, Ascend, Lucent, Fore, etc. So each of these too has the potential to lock-up and need rebooting, and each of these is very inconvenient to staff or visit for a manual reboot when needed.
Server Technology, Inc., of Reno, Nev., markets a 48-VDC remote power manager and intelligent power distribution unit that provides for remote rebooting of remote digital subscriber line access multiplexers and other network equipment in telco central offices and router farms. The SENTRY 48-VDC is a network management center that eliminates the dispatching of field service technicians to cycle power and rectify locked-up digital subscriber line access multiplexers.
Statistics show that seventy percent or more of all network equipment lock-ups can be overcome by rebooting, for example, cycling power off and on. A remote power controller, like the SENTRY, can reduce network outages from hours to minutes.
In a typical installation, the telco central office provides the competitive local exchange carriers with bare rack space and a 48-VDC power feed cable that can supply 60-100 amps. The single power input is conventionally distributed through a fuse panel to several digital subscriber line access multiplexers in a RETMA-type equipment rack. Individual fuses in such fuse panel are used to protect each DSLAM from power faults.
But such fuses frequently weld themselves to their sockets in the fuse panel due to loose contacts and high amperage currents. It is ironic therefore that many digital subscriber line access multiplexers do not have power on/off switches. Thus the fuse often must be pried out and put back in or replaced so the DSLAM can be powered-off for rebooting. But when the fuse is welded, removing the fuse without damaging the fuse panel can be nearly impossible.
The Server Technology SENTRY 48-VDC accepts from the telco or other site host an A-power feed cable and B-power feed cable. Internally, DC-power is distributed to a set of “A” and “B” rear apron output terminal blocks that are protected by push-to-reset circuit breakers. The fuse panel is no longer required. The A-feed and B-feed are then matched to the newer digital subscriber line access multiplexers that also require A-power supply and B-power supply inputs.
Sometimes digital signaling lines can lose the carrier. In such cases, the respective DSLAM must be rebooted to restore the DS3 line. A technician is conventionally required to visit the DSLAM, and use a console port to monitor how the software reboots, and if communications are correctly restored to the DS3.
A SENTRY 48-VDC can be used to remotely power-off the digital subscriber line access multiplexer in the event the carrier is lost. A companion asynchronous communications switch can be used to establish a connection to the DSLAM's console port. Power can be cycled to the DSLAM, and the asynchronous communications switch used to monitor the reboot operation to make certain that the carrier to the DS3 line is restored. The asynchronous communications switch is a low-cost alternative to the expensive terminal server typically used for console port access. The reboot process and the console port monitoring process can both be managed from an operations center, without the need to dispatch technical personnel to the remote location.
The floor space that a competitive local exchange carrier's equipment rack sits upon is very expensive, so the equipment placed in the vertical space in a rack (“U-space”) must be as compact as possible. A typical rack may house several digital subscriber line access multiplexers, a terminal server, a fuse panel, and 48-VDC modems. A SENTRY 48-VDC uses “2 U or 3 U” (3.5 or 5.25 inches) of vertical RETMA-rack space, and combines the functions of a fuse panel, a terminal server, and a modem. As many as sixteen 10-amp devices, eight 20 amp devices, or four 35-amp devices can be supported.
Power controllers, like the Server Technology SENTRY, have long used electro-mechanical relays to open and close the 48-volt supply lines to the network equipment. Unfortunately, the same physical phenomena that welds the fuses in their holders can also weld or destroy the contacts of these relays.
Most electric welders generate the high heats necessary to fuse metal together by arcing a direct current (DC) low voltage (under 50-volts) and high current (over 50-amps) across an electrode gap. Such conditions occur in a power controller's relay, especially when the relay contacts are opening. The mass inertia of the contact mechanism has to be overcome before the contacts can open. The contacts accelerate apart, but are moving only very slowly at the start. Electric arcs, once generated, will continue even though the electrode separation distance is increased. This is the so-called Jacob's Ladder effect. The ionized air and the heated contacts increase the distance an arc can bridge. The arcing stops only after the contacts are very wide apart.
In contrast, a pair of open relay contacts will not arc until the contacts get very close to one another. By this time, the contact closure is moving at its near maximum velocity. So the remaining gap that needs to be closed up when the arc commences will vanish quickly.
One prominent prior art arc suppression circuit consists of a capacitor in series with a resistor and a diode in parallel interconnecting the input and the output of the electro-mechanical relay. This type of conventional circuit shunts some electricity around the electro-mechanical relay when it is activated, reducing the extent of arcing that might otherwise take place. This conventional circuit is, however, relatively slow acting circuit (in passive response to the activation of the electro-mechanical relay to open or stop the flow of current from, for example, the input to the output) and does not completely eliminate all arcing between separating contacts in an electro-mechanical relay. Over an extended period of activation of this type of electro-mechanical relay circuit with passive arc suppression, electro-mechanical relay contacts often burn up and fail.